Semiconductor device, method of manufacturing the same, and apparatus for manufacturing semiconductor

ABSTRACT

A semiconductor device includes a plurality of photoelectric conversion photodiodes provided on a silicon substrate, and a refractive index matching film provided on each of the photodiodes. The refractive index matching film is composed of an insulating compound layer represented by SiO x N y  (0≦x and y) assuming that the molar ratio of silicon, oxygen and nitrogen of the compound layer is 1:x:y. The oxygen content of the compound layer is the lowest at the silicon interface with each photodiode and the highest in an upper portion of the compound layer, and the nitrogen content is the highest at the silicon interface with each photodiode and the lowest in the upper portion of the compound layer. Therefore, multiple reflection can be decreased to improve light receiving sensitivity, as compared with a case in which a SiN single layer and a SiO 2  single layer are laminated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates a semiconductor device suitablyused for a photoelectric transducer such as a photocoupler or the like,a solid-state imaging device or field-effect imaging device comprising asemiconductor image sensor which receives light incident on an on-chiplens formed on a color filter, a method of manufacturing thesemiconductor device, and an apparatus for manufacturing asemiconductor.

[0003] More specifically, a refractive index matching film is providedon a photoelectric conversion light-receiving element, and a compositioncomposed of silicon, oxygen and nitrogen which constitute the refractiveindex matching film is adjusted so that the refractive index of acompound layer constituting the refractive index matching filmcontinuously changes from the refractive index of a silicon oxide filmof 1.45 to the refractive index of a silicon nitride film of 2.0. As aresult, reflection from the light receiving element can be minimized,and light receiving sensitivity can be improved.

[0004] 2. Description of the Related Art

[0005] In recent years, a video camera and a digital still camera havebeen increasingly used in many schools, homes and broadcast stations.Such a camera requires a solid-state imaging device. The solid-stateimaging device comprises CCD (Charge Coupled Device) imaging devicesarranged as photoelectric transducers in a two-dimensional form. The CCDimaging device means a semiconductor device having a structure in whichunit elements each comprising a photodiode and a MOS capacitor areregularly arranged. The solid-state imaging device has the function tomove a group of charges stored in the surface of a semiconductorsubstrate along the array direction of electrodes of the MOS capacitors.

[0006] Namely, the solid-state imaging device comprises pluralities ofphotodiodes, MOS capacitors, vertical transfer registers, horizontaltransfer registers, and charge detecting amplifiers, which are providedon the semiconductor substrate. When light is applied to a lightreceiving surface of the solid-state imaging device, the light isconverted into signal charges by the photodiodes, and then stored in theMOS capacitors. The signal charges stored in the MOS capacitors aretransferred by the vertical transfer registers (referred to as “verticalCCD sections” hereinafter) and horizontal transfer registers, andfinally detected by the charge detecting amplifiers and read as analoguereceived signals.

[0007]FIG. 14 is a sectional view showing an example of a configurationof a solid-state imaging device 10 of a first conventional example. Asshown in FIG. 14, a semiconductor buried layer (P-WELL) 1 is formed on aN-type silicon substrate 11, the P-WELL 1 comprising photodiodes PD eachhaving a N-type impurity region (impurity diffused layer) 2, andvertical CCD sections 12 each having a N-type impurity region (impuritydiffused layer) 3. The P-WELL 1 further comprises transfer gate sections13 for reading out signal charges from the photodiodes PD to thevertical CCD sections 12, to isolate the silicon substrate 11.

[0008] The N-type impurity region 2 constituting each of the photodiodesPD is isolated from the N-type impurity region 3 constituting thecorresponding vertical CCD section 12 by a channel stopper 4 comprisinga P-type impurity region. Furthermore, a transfer electrode 17 isprovided on each of the vertical CCD sections 12 through a gateinsulating film (silicon oxide film) 14.

[0009] The transfer electrodes 17 of the vertical CCD sections 12 arecovered with a shielding film 19 composed of aluminum or tungstenthrough an interlayer insulating film 18. The shielding film 19 hasapertures formed above the photodiodes PD to define light-receivingwindows 21. The shielding film 19 is coated with a cover film 22comprising a silicon oxide film of PSG or the like. Furthermore, aplanarizing film 23, a color filter 24, and microlenses 25 are formed inorder on the cover film 22.

[0010] The material of the cover film 22 is not limited to the siliconoxide film, and an example using a silicon nitride film is also known.For example, the technical document, Japanese Unexamined PatentApplication Publication No. 60-177778, discloses that a plasma siliconnitride film is formed on a transparent electrode composed ofpolycrystalline silicon. However, in such a structure in which a siliconnitride film is deposited, an increase in short-wavelength sensitivityis expected due to a multiple interference effect.

[0011] Therefore, in the structure shown in FIG. 14 in which the siliconinterfaces of the photodiodes PD are covered directly with the coverfilm 22, a loss of incident light is increased due to surface reflectionfrom the N-type silicon substrate 11 to fail to obtain sufficient lightreceiving sensitivity.

[0012] In addition, in the structure in which the plasma silicon nitridefilm is formed below the planarizing film 23, ripple occurs in spectraltransmittance due to an interference effect between a silicon nitridefilm serving as the interlayer insulating film 18 and a silicon nitridefilm serving as the gate insulating film 14 provided below theinterlayer insulating film 18. Therefore, the spectral characteristicsof the color filter layer 24 easily vary.

[0013] In order to solve the above-described problem, for example,Patent Publication No. 3196727 discloses a technique for forming ananti-reflection film on photodiodes PD. FIG. 15 is a sectional viewshowing an example of a construction of a solid-state imaging device 10′of a second conventional example.

[0014] The solid-state imaging device 10′ shown in FIG. 15 comprises aN-type silicon substrate 11 on a surface of which photodiodes PD areformed for obtaining signal charges. Each of the photodiodes PDcomprises a N-type impurity region (impurity diffused region) 2.

[0015] Furthermore, a silicon oxide thin film serving as a gateinsulating film 14 is formed on the silicon substrate 11, and a siliconnitride film serving as an anti-reflection thin film 15 having arefractive index higher than that of the silicon oxide film 14 and lowerthan that of the silicon substrate 11 is formed on the silicon oxidethin film 14. The refractive index of the silicon oxide film 14 is about1.45, and the refractive index of the silicon nitride film is about 2.0.Assuming that the refractive index is n, the thickness t of each of thesilicon oxide film and the silicon nitride film is set to satisfy therelationship 350/(4n) nm≦t≦450/(4n) nm. These films 14 and 15 are formedfor preventing a dark current.

[0016] When the thickness of each of the silicon oxide film and thesilicon nitride film is set as described above, the anti-reflection film15 having relatively flat reflection in the visible light region can beobtained. By appropriately setting the thickness of each of the siliconoxide film and the silicon nitride film, reflectance can be suppressedto an average of about 12 to 13%, and is thus suppressed to about ⅓ ofthe reflectance of the conventional silicon substrate 11 of about 40%.

[0017] Like in the first conventional example, transfer electrodes 17are formed on the vertical CCD sections 12 through a silicon oxide film.Furthermore, a shielding film 19 composed of aluminum or tungsten isdeposited through an interlayer insulating film 18, the shielding film19 having apertures respectively formed above the photodiodes PD.

[0018] A cover film 22 is formed on the shielding film 19. The coverfilm 22 comprises a PSG film serving as a silicon-based passivationfilm, and has a refractive index of about 1.46. In addition, aplanarizing layer 23, a filter layer 24, and microlenses 25 are formedon the cover film 22. The refractive index of the color filter layer 24is about 1.5 to 1.6, and is thus substantially the same as thepassivation film.

[0019] However, the solid-state imaging device (simply referred to asthe “semiconductor device” hereinafter) 10′ of the second conventionalexample shown in FIG. 15 has the following problems:

[0020] (1) The refractive index of the cover film 22 formed above theanti-reflection film (silicon nitride film) 15 is about 1.4 to 1.6, andis greatly different from the refractive index 2.0 of the siliconnitride film serving as the anti-reflection film 15. Therefore,reflection occurs between the anti-reflection film 15 and the cover film22.

[0021] (2) The reflection between the anti-reflection film 15 and thecover film 22 is associated with reflection from the photodiodes (lightreceiving elements) PD, thereby causing a smear and inhibiting animprovement in light receiving sensitivity.

SUMMARY OF THE INVENTION

[0022] The present invention has been achieved for solving the aboveproblems, and an object of the present invention is to provide asemiconductor device having a structure in which refractive indexmatching between upper and lower films is controlled so as to minimizereflection from a light receiving element and to improve light receivingsensitivity, a method of manufacturing the semiconductor device, and anapparatus for manufacturing a semiconductor.

[0023] In an aspect of the present invention, a semiconductor devicecomprises a substrate, and a compound layer provided on the substrate,wherein the compound layer is represented by SiO_(x)N_(y) (0≦x and y)assuming that the molar ratio of silicon, oxygen and nitrogen of thecompound layer is 1:x:y, the oxygen content is the lowest near theinterface with the substrate and the highest in an upper portion of thecompound layer, and the nitrogen content is the highest near theinterface with the substrate and the lowest in the upper portion of thecompound layer.

[0024] In another aspect of the present invention, a semiconductordevice comprises a semiconductor substrate, and an insulating compoundlayer provided on the semiconductor substrate, wherein the insulatingcompound layer is represented by SiO_(x)N_(y) (0≦x and y) assuming thatthe molar ratio of silicon, oxygen and nitrogen of the insulatingcompound layer is 1:x:y, the oxygen content is the lowest at theinterface with the semiconductor substrate and the highest in au upperportion of the insulating compound layer, and the nitrogen content isthe highest at the interface with the semiconductor substrate and thelowest in the upper portion of the insulating compound layer.

[0025] In a further aspect of the present invention, a semiconductordevice for photoelectrically converting received light to output areceived light signal comprises a semiconductor substrate, a pluralityof photoelectric conversion light receiving elements provided on thesemiconductor substrate, and a refractive index matching film providedon the light receiving elements, wherein the refractive index matchingfilm comprises an insulating compound layer represented by SiO_(x)N_(y)(0≦x and y) assuming that the molar ratio of silicon, oxygen andnitrogen of the compound layer is 1:x:y, the oxygen content of thecompound layer is the lowest at the interface with each light receivingelement and the highest in au upper portion of the compound layer, andthe nitrogen content of the compound layer is the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.

[0026] In a still further aspect of the present invention, a method ofmanufacturing a semiconductor device for photoelectrically convertingreceived light to output a received light signal comprises a step offorming a plurality of photoelectric conversion light receiving elementson a semiconductor substrate, and a step of forming a refractive indexmatching film on each of the light receiving elements formed on thesemiconductor substrate, wherein the refractive index matching filmcomprises an insulating compound layer represented by SiO_(x)N_(y) (0≦xand y) assuming that the molar ratio of silicon, oxygen and nitrogen ofthe insulating compound layer is 1:x:y, the oxygen content of thecompound layer is the lowest at the interface with each light receivingelement and the highest in au upper portion of the compound layer, andthe nitrogen content of the compound layer is the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.

[0027] In a further aspect of the present invention, an apparatus formanufacturing a semiconductor device for photoelectrically convertingreceived light to output a received light signal comprises a formationmeans for forming a plurality of photoelectric conversion lightreceiving elements on a semiconductor substrate, and a deposition meansfor depositing a refractive index matching film on each of the lightreceiving elements formed on the semiconductor substrate, wherein indepositing the refractive index matching film by the deposition means,an insulating compound layer represented by SiO_(x)N_(y) (0≦x and y)assuming that the molar ratio of silicon, oxygen and nitrogen of theinsulating compound layer is 1:x:y is deposited so that the oxygencontent of the compound layer is the lowest at the interface with eachlight receiving element and the highest in an upper portion of thecompound layer, and the nitrogen content of the compound layer is thehighest at the interface with each light receiving element and thelowest in the upper portion of the compound layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a sectional view showing an example of a structure of aphotoelectric transducer according to a first embodiment of the presentinvention;

[0029]FIG. 2 is a conceptual diagram showing an example of a structureof an insulating compound layer represented by SiO_(x)N_(y) (0≦x and y);

[0030]FIG. 3 is a conceptual diagram showing an example of arelationship between the oxygen and nitrogen contents of the insulatingcompound layer shown in FIG. 2;

[0031]FIG. 4 is a block diagram showing an example of a configuration ofa semiconductor manufacturing apparatus according to an embodiment ofthe present invention;

[0032]FIGS. 5A and 5B are drawings respectively showing steps in anexample of formation of the photoelectric transducer of the firstembodiment of the present invention;

[0033]FIGS. 6A and 6B are drawings respectively showing steps performedafter the step shown in FIG. 5B;

[0034]FIGS. 7A and 7B are drawings respectively showing steps performedafter the step shown in FIG. 6B;

[0035]FIGS. 8A and 8B are drawings respectively showing steps performedafter the step shown in FIG. 7B;

[0036]FIG. 9 is a sectional view showing an example of a structure of aphotoelectric transducer according to a second embodiment of the presentinvention;

[0037]FIGS. 10A and 10B are drawings respectively showing steps in anexample of formation of the photoelectric transducer of the secondembodiment of the present invention;

[0038]FIGS. 11A and 11B are drawings respectively showing stepsperformed after the step shown in FIG. 10B;

[0039]FIGS. 12A and 12B are drawings respectively showing stepsperformed after the step shown in FIG. 11B;

[0040]FIGS. 13A and 13B are drawings respectively showing stepsperformed after the step shown in FIG. 12B;

[0041]FIG. 14 is a sectional view showing a structure of a solid-stateimaging device of a first conventional example; and

[0042]FIG. 15 is a sectional view showing a structure of a solid-stateimaging device of a second conventional example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] A semiconductor device, a manufacturing method therefor, and asemiconductor manufacturing apparatus according to embodiments of thepresent invention will be described below with reference to thedrawings.

[0044] First Embodiment

[0045]FIG. 1 is a sectional view showing an example of a structure of aphotoelectric transducer 100 according to a first embodiment of thepresent invention.

[0046] In this embodiment, a refractive index matching film is providedon each of photoelectric conversion light receiving elements, and therefractive index matching film comprises an insulating compound layerrepresented by SiO_(x)N_(y) (0≦x and y) assuming that the molar ratio ofsilicon, oxygen and nitrogen of the insulating compound layer is 1:x:y.In addition, the oxygen content of the compound layer is the lowest atthe interface with each light receiving element and the highest in anupper portion of the compound layer, and the nitrogen content of thecompound layer is the highest at the interface with each light receivingelement and the lowest in the upper portion of the compound layer.

[0047] In this embodiment, the refractive index of the compound layerserving as the refractive index matching film is continuously changedfrom the refractive index of a silicon oxide film of 1.45 to therefractive index of a silicon nitride film of 2.0, to minimizereflection from each light receiving element and improve light receivingsensitivity.

[0048] The photoelectric transducer 100 shown in FIG. 1 is an example ofsemiconductor devices for photoelectrically converting received light tooutput received light signals. The photoelectric transducer 100 ispreferably applied to a photocoupler, a solid-state imaging device orfield-effect imaging device comprising a solid-state imaging devicewhich receives light incident from on-chip lenses provided on a colorfilter.

[0049] The photoelectric transducer 100 comprises a N-type siliconsubstrate (N-sub) 11 as an example of a semiconductor substrate. Thesilicon substrate 11 comprises a plurality of HAD (Hole AccumulatedDiode) sensors (simply referred to as “photodiodes PD” hereinafter) asan example of photoelectric conversion light receiving elements. In thisembodiment, the photodiode PD (charge coupled imaging device) of onepixel is described.

[0050] In the photoelectric transducer 100, a P-type impurity buriedlayer (P-WELL) 1 is provided on the N-type silicon substrate 11. TheP-WELL 1 contains a photodiode PD comprising a N-type impurity region(layer) 2, and a vertical CCD (vertical transfer register) section 12comprising a N-type impurity region (layer) 3. Furthermore, thephotodiode PD is separated from the vertical CCD section 12 by atransfer gate 13 so as to read a signal charge from the photodiode PD tothe vertical CCD section 12.

[0051] Furthermore, a silicon oxide film (SiO₂ film) serving as a gateinsulating film 14 having a predetermined thickness is provided abovethe interface of the silicon substrate 11, and a silicon nitride film(Si₃N₄ film) serving as an antireflection film 15 is provided on thegate insulating film 14. The thickness t of each of the gate insulatingfilm 14 and the anti-reflection film 15 is defined in the range of 10nm≦t≦40 nm. The thickness of each of the two films is preferably set toabout 25 to 35 nm. By selecting the thickness t within this range, noadverse effect of reflection occurs, and a dark current can be preventedto prevent stress in film formation.

[0052] Furthermore, a refractive index matching film 16 having athickness of about 1.0 μm to 2.0 μm is provided on the surface of theanti-refection film (silicon nitride film) 15 including the portionabove the photodiode PD. The gate insulating film 14 and theanti-reflection film 15 are sandwiched between the photodiode PD and therefractive index matching film 16. The refractive index matching film 16comprises an insulating compound layer represented by SiO_(x)N_(y) (0≦xand y) assuming that the molar ratio of silicon, oxygen and nitrogen ofthe insulating compound layer is 1:x:y. The oxygen content of theinsulating compound layer is the lowest at the silicon interface withthe photodiode PD and the highest in an upper portion of the compoundlayer, and the nitrogen content of the insulating compound layer is thehighest at the silicon interface with the photodiode PD and the lowestin the upper portion of the compound layer.

[0053] The refractive index matching film 16 comprises the bottomcomposed of silicon nitride, and the top composed of silicon oxide.Although the insulating compound layer may comprise a plurality ofinsulating layers having a constant thickness, the insulating compoundlayer preferably comprises layers having thicknesses continuouslyvarying to satisfy the above-described conditions of the nitrogen andoxygen contents. In this case, reflection within the layer can beminimized.

[0054] In the refractive index matching film 16, the oxygen content ofthe compound layer is defined in the range of 0≦x<2 so that the oxygencontent is the lowest at the silicon interface with the photodiode PDand the highest in the upper portion, and the nitrogen content of thecompound layer is defined in the range of 0≦y<4/3 so that the nitrogencontent is the highest at the silicon interface with the photodiode PDand the lowest in the upper portion.

[0055] Namely, in the compound layer, oxygen is continuously distributedbased on the oxygen content condition of 0≦x<2 so that the oxygencontent is the lowest at the silicon interface with the photodiode PDand the highest in the upper portion. Also, in the compound layer,nitrogen is continuously distributed based on the nitrogen contentcondition of 0≦y<4/3 so that the nitrogen content is the highest at thesilicon interface with the photodiode PD and the lowest in the upperportion.

[0056] The insulating compound layer is preferably deposited by alow-pressure CVD apparatus. During deposition, an oxygen gas flow rateis controlled according to a continuous increasing function (includingprimary and secondary functions). At the same time, a nitrogen gas flowrate is controlled according to a decreasing function (including primaryand secondary functions). In this embodiment, the compound layerrepresented by SiO_(x)N_(y) satisfies 4=2x+3y, and x increases from thebottom to the top.

[0057] Furthermore, a transfer electrode 17 is formed on the verticalCCD section 12 through the gate insulating film (silicon oxide film) 14.The transfer electrode 17 is covered with a shielding film 19 composedof aluminum or tungsten through an interlayer insulating film 18. Theshielding film 19 has an aperture formed above the photodiode PD. Theaperture functions as a light receiving window 21. The shielding film 19is coated with a cover film 22 comprising a silicon oxide film of PSG orthe like.

[0058]FIG. 2 is a conceptual diagram showing an example of a structureof an insulating compound layer 16′ represented by SiO_(x)N_(y) (0≦x andy). In FIG. 2, the refractive index matching film 16 comprises theinsulating compound layer 16′ represented by SiO_(x)N_(y) (0≦x and y).The refractive index matching film 16 is formed by patterning theinsulating compound layer 16′, and comprises the bottom composed ofsilicon nitride (Si₃N₄). The refractive index of a silicon nitride filmis about 2.0, and is higher than that of a silicon oxide film.

[0059] The silicon nitride film is generally formed by SiH₄ gas andammonia gas used as raw material gases according to chemical reactionrepresented by the following formula (1):

3SiH₄+4NH₃→Si₃N₄+12H₂  (1)

[0060] The top of the refractive index matching film 16 comprisessilicon oxide (SiO₂). The refractive index of a silicon oxide film isabout 1.45. The silicon oxide film is generally formed by SiH₄ gas andO₂ gas used as raw material gases according to chemical reactionrepresented by the following formula (2):

SiH₄+2O₂→SiO₂+2H₂O  (2)

[0061] In the insulating compound layer 16′ represented by SiO_(x)N_(y)(0≦x and y), the film quality continuously (in analog) changes betweenthe bottom composed of silicon nitride and the top composed of siliconoxide. The refractive index of the compound layer 16′ continuouslychanges from the refractive index of the silicon oxide film of 1.45 tothe refractive index of the silicon nitride film of 2.0. This is optimumfor the refractive index matching film 16.

[0062]FIG. 3 is a conceptual diagram showing an example of therelationship between the oxygen and nitrogen contents of the insulatingcompound layer 16′ represented by SiO_(x)N_(y) (0≦x and y). In FIG. 3,the oxygen (O₂) and nitrogen (N₂) contents (%) are shown on theordinate, and the deposition position in the deposition direction andrefractive index of the insulating compound layer 16′ are shown on theabscissa.

[0063] The insulating compound layer 16′ is preferably deposited byusing a low-pressure CVD apparatus. During deposition, as shown in FIG.3, an oxygen gas flow rate is controlled according to a continuousincreasing function (including primary and secondary functions). At thesame time, a nitrogen gas flow rate is controlled according to adecreasing function (including primary and secondary functions). In thisembodiment, the compound layer 16′ represented by SiO_(x)N_(y) satisfies4=2x+3y, and x increases from the bottom to the top.

[0064] Therefore, in the photoelectric transducer 100 of the firstembodiment of the present invention, the refractive index of thecompound layer 16′ serving as the refractive index matching film 16 canbe continuously changed from the refractive index of the silicon oxidefilm of 1.45 to the refractive index of the silicon nitride film of 2.0,as compared with a case in which a silicon nitride single film and asilicon oxide single film are simply laminated. Therefore, a boundarybetween the silicon nitride film and the silicon oxide film can beremoved, thereby minimizing reflection from the photodiode PD.

[0065] Therefore, multiple reflection is decreased to improve lightreceiving sensitivity, as compared with the case in which the siliconnitride single film and the silicon oxide single film are simplylaminated. Furthermore, diffused reflection due to multiple reflectioncan be suppressed to improve a smear. The refractive index matching film16 comprising the insulating compound layer 16′ causes no stress, andthus causes less dark current. Semiconductor manufacturing apparatusFIG. 4 is a block diagram showing an example of a configuration of asemiconductor manufacturing apparatus 300 according to an embodiment ofthe present invention.

[0066] The semiconductor manufacturing apparatus 300 shown in FIG. 4 isan apparatus for manufacturing the photoelectric transducer 100 shown inFIG. 1, and the like. In the semiconductor manufacturing apparatus 300,a plurality of photoelectric conversion photodiodes PD are previouslyformed on the silicon substrate 11 by a formation means 41 such as anion implantation apparatus or the like. Then, the refractive indexmatching film 16 is deposited each the photodiode PD by a low-pressureCVD apparatus 30 as an example of deposition means.

[0067] The low-pressure CVD apparatus 30 comprises a chamber 31 in whicha dispersion head 32 for discharging a raw material gas, and a susceptor33 for mounting a wafer thereon are provided. Also, an exhaust treatmentmeans 34, a shutter 35 for inserting and discharging the wafer, rawmaterial gas cylinders 36A to 36C, gas regulating valves 37A to 37C, anda control device 38 are provided outside the chamber 31.

[0068] The shutter 35 is connected to the control device 38 so that theshutter 35 is controlled to be opened and closed for inserting anddischarging the semiconductor wafer 11′ into and from the chamber 31.The exhaust treatment means 34 is also connected to the control device38 so that the exhaust treatment means 34 is controlled to evacuate thechamber 31 and discharge exhaust gas. The semiconductor wafer 11′ ismounted on the susceptor 33, and the control device 38 is connected tothe susceptor 33 so as to heat the semiconductor wafer 11′ to apredetermined temperature and cool the semiconductor wafer 11′. Also,the dispersion head 32 is provided above the susceptor 33 in the chamber31 to emit raw material gases A, B and C. As the raw material gases A, Band C, SiH₄, NH₃, O₂, and the like can be used.

[0069] A supply port of the dispersion head 32 is extended to theoutside of the chamber 31, and connected to the raw material gascylinders 36A to 36C through the gas regulating valves 37A to 37C,respectively. The raw material gas cylinders 36A, 36B and 36C are filledwith the raw material gases A, B and C, respectively. The gas regulatingvalves 37A to 37C can be operated by the control device 38 by remotecontrol. The control device 38 remote-controls the gas regulating valve37A to regulate a flow rate of the raw material gas A, remote-controlsthe gas regulating valve 37B to regulate a flow rate of the raw materialgas B, and remote-controls the gas regulating valve 37C to regulate aflow rate of the raw material gas C.

[0070] In forming the refractive index matching film 16 shown in FIG. 1,the control device 38 controls the deposition of the insulating compoundlayer 16′ represented by SiO_(x)N_(y) (0≦x and y) assuming that themolar ratio of silicon, oxygen and nitrogen of the insulating compoundlayer 16′ is 1:x:y so that the oxygen content of the insulating compoundlayer 16′ is the lowest at the silicon interface with the photodiode PDand the highest in an upper portion of the compound layer 16′, and thenitrogen content of the insulating compound layer 16′ is the highest atthe silicon interface with the photodiode PD and the lowest in the upperportion of the compound layer 16′.

[0071] In this embodiment, in order that the oxygen content of thecompound layer 16′ is the lowest at the silicon interface with thephotodiode PD, and is the highest in the upper portion, the oxygencontent of the compound layer 16′ is previously set to 0≦x<2. Also, inorder that the nitrogen content of the compound layer 16′ is the highestat the silicon interface with the photodiode PD, and is the lowest inthe upper portion, the nitrogen content of the compound layer 16′ ispreviously set to 0≦y<4/3. The refractive index matching film 16 isdeposited based on these settings.

[0072] Next, an example of an operation of the semiconductormanufacturing apparatus 300 will be described. In this example, aplurality of photoelectric conversion photodiodes PD are previouslyformed on the semiconductor wafer (silicon substrate) 11′ by theformation means 41 such as the ion implantation apparatus. Then, thesemiconductor wafer 11′ is transferred from the formation means 41 tothe low-pressure CVD apparatus 30, and the refractive index matchingfilm 16 is formed on each of the photodiodes PD formed on thesemiconductor wafer 11′.

[0073] On the assumption that the refractive index matching film 16 isdeposited, the control device 38 controls the shutter 35 to open andclose it, and the semiconductor wafer 11′ is transferred into thechamber 31 and mounted on the susceptor 33. Then, the control device 38controls the exhaust treatment means 34.to exhaust air from the chamber31 to form a vacuum in the chamber 31. The temperature of the susceptor33 is controlled by the control device 38 to, for example, heat thesemiconductor wafer 11′ to a predetermined temperature.

[0074] Then, the gas regulating valves 37A to 37C are remote-controlledby the control device 38 to emit the raw material gases A, B and C fromthe dispersion head 32 provided above the susceptor 33 in the chamber31. The raw material gases A, B and C include SiH₄, NH₃, O₂, and thelike.

[0075] In the chamber 31, a vapor phase reaction I of the raw materialgases A, B and C takes place, and a surface reaction II takes place onthe semiconductor wafer 11′ according to the above-described formulas(1) and (2). The exhaust gas is discharged to the outside by the exhausttreatment means 34.

[0076] For example, when the molar ratio 1:x:y of silicon, oxygen andnitrogen, and the deposition time are set by the control device 38, thegas regulating valve 37C is controlled according to the continuousincreasing function (including primary and secondary functions) shown inFIG. 3 to regulate the flow rate of oxygen gas. At the same time, thegas regulating valve 37B is controlled according to the continuousdecreasing function (including primary and secondary functions) shown inFIG. 3 to regulate the flow rate of nitrogen gas (NH₃).

[0077] In this control operation, the oxygen content of the compoundlayer 16′ is set to the lowest at the silicon interface with eachphotodiode PD, and the highest in the upper portion, and the oxygen flowrate is continuously regulated based on the oxygen content of 0≦x<2 inthe compound layer 16′. Also, the nitrogen content of the compound layer16′ is set to the highest at the silicon interface with each photodiodePD, and the lowest in the upper portion, and the nitrogen flow rate iscontinuously regulated based on the nitrogen content of 0≦y<4/3 in thecompound layer 16′.

[0078] Consequently, the insulating compound layer 16′ represented bySiO_(x)N_(y) (0≦x and y) is deposited for the refractive index matchingfilm 16 so that the oxygen content of the compound layer 16′ is thelowest at the silicon interface with each photodiode PD and the highestin the upper portion of the compound layer 16′, and the nitrogen contentof the compound layer 16′ is the highest at the silicon interface witheach photodiode PD and the lowest in the upper portion of the compoundlayer 16′.

[0079] In this way, the semiconductor manufacturing apparatus 300 of thepresent invention is capable of manufacturing a semiconductor device 100with high reproducibility, in which the refractive index of the compoundlayer 16′ serving as the refractive index matching film 16 iscontinuously changed from the refractive index of a silicon oxide filmof 1.45 to the refractive index of a silicon nitride film of 2.0, ascompared with the case in which a silicon nitride single film and asilicon oxide single film are simply laminated to form the semiconductordevice 100. Therefore, the semiconductor device 100 with highreliability can be manufactured.

[0080] Method of Manufacturing Semiconductor Device

[0081] FIGS. 5 to 8 are drawings showing steps in an example of theformation of the photoelectric transducer 100 of the first embodiment ofthe present invention.

[0082] This embodiment is based on the condition that the photoelectrictransducer 100 comprising the gate insulating film 14, theanti-reflection film 15 and the refractive index matching film 16 shownin FIG. 1 is manufactured. Under this manufacturing condition, thesilicon substrate 11 (semiconductor wafer 11′) having the transferelectrodes 17, the photoelectric conversion photodiodes PD, the gateinsulating film 14 and the anti-reflection film 15 shown in FIG. 5A isfirst prepared. In the semiconductor wafer 11′, a predetermined impurityis implanted into the N-type silicon substrate 11 shown in FIG. 5A toform the P-type semiconductor buried layer (P-WELL) 1 in which thephotodiodes PD each comprising the N-type impurity region (layer) 2 andthe vertical CCD sections 12 each comprising the N-type impurity region(layer) 3 are formed.

[0083] In this structure, the transfer gate section 13 is formed as aregion for reading a signal charge from each of the photodiodes PD tothe corresponding vertical CCD section 12. In this example, a siliconoxide film having a predetermined thickness is formed on each of thephotodiodes PD before the refractive index matching film 16 is formed oneach photodiode PD. The thickness t of the silicon oxide film is definedin the range of 10 nm≦t≦40 nm, and preferably set to 30 nm. By settingthe thickness to this value, reflection and stress can be prevented.Furthermore, polysilicon is deposited over the entire surface of thegate insulating film 14, and then selectively etched to form thetransfer electrodes 17.

[0084] Then, as shown in FIG. 5B, the semiconductor wafer 11′ isre-oxidized to form the interlayer insulating film 18 comprising asilicon oxide film. The transfer electrodes 17 can be isolated by theinterlayer insulating film 18. Then, as shown in FIG. 6A, the insulatingcompound layer 16′ is selectively formed over the entire surface of thesemiconductor wafer 11′ to form the refractive index matching films 16.Since the thickness of the compound layer 16′ must be strictlycontrolled, the compound layer 16′ is formed by the low-pressure CVDapparatus 30 shown in FIG. 4. Each of the refractive index matchingfilms 16 comprises the bottom composed of silicon nitride in contactwith the silicon interface with each photodiode PD, and the top composedof silicon oxide.

[0085] Therefore, each of the refractive index matching films 16comprises the insulating compound layer 16′ represented by SiO_(x)N_(y)(0≦x and y) assuming that the molar ratio of silicon, oxygen andnitrogen of the insulating compound layer 16′ is 1:x:y. In addition, theoxygen content of the compound layer 16′ is the lowest at the siliconinterface with each photodiode PD and the highest in the upper portionof the compound layer 16′, and the nitrogen content of the compoundlayer 16′ is the highest at the interface with each photodiode PD andthe lowest in the upper portion of the compound layer 16′.

[0086] In forming the refractive index matching films 16, in order toset the oxygen content of the compound layer 16′ to the lowest at thesilicon interface with each photodiode PD and the highest in the upperportion of the compound layer 16′, the oxygen content in the compoundlayer 16′ is defined in the range of 0≦x<2. Similarly, in order to setthe nitrogen content of the compound layer 16′ to the highest at theinterface with each photodiode PD and the lowest in the upper portion ofthe compound layer 16′, the nitrogen content in the compound layer 16′is defined in the range of 0≦y<4/3.

[0087] In order to continuously change the oxygen and nitrogen contentsof the compound layer 16′, the nitrogen and oxygen flow rates in thelow-pressure CVD apparatus 30 may be continuously changed during theformation of the film 16. Namely, in order to set the oxygen content ofthe compound layer 16′ to the lowest at the silicon interface with eachphotodiode PD and the highest in the upper portion of the compound layer16′, the oxygen flow rate is regulated to continuously distribute basedon the oxygen content of 0≦x<2 in the compound layer 16′.

[0088] In order to set the nitrogen content of the compound layer 16′ tothe highest at the silicon interface with each photodiode PD and thelowest in the upper portion of the compound layer 16′, the nitrogen flowrate is regulated to continuously distribute based on the oxygen contentof 0≦y<4/3 in the compound layer 16′. In this example, the compoundlayer represented by SiO_(x)N_(y) satisfies 4=2x+3y, and x increasesfrom the bottom to the top.

[0089] Then, as shown in FIG. 6A, a resist film 42 formed on thecompound layer 16′ is selectively patterned as follows. First, a resistmaterial is coated over the entire surface of the compound layer 16′,and then exposed and developed by using, as a mask, a reticle having apredetermined aperture pattern formed by baking. The aperture patternhas a shape for forming the light receiving windows 21 (not shown) abovethe photodiodes PD. Then, the excessive resist material is removed topattern the resist film 42.

[0090] Then, the compound layer 16′ is selectively etched through theresist film 42 used as the mask. The etching may be wet etching or dryetching. The wet etching is performed with an etchant comprising dilutedhydrofluoric acid or phosphoric acid. As a result, as shown in FIG. 6B,the compound layer 16′ (film) can be left only above each of thephotodiodes PD, to form the refractive index matching films 16.

[0091] Then, as shown in FIG. 7A, aluminum or tungsten used as amaterial 19′ for the shielding film 19 is deposited over the entiresurface of the silicon substrate 11 by the same method as a conventionalmethod. Then, as show in FIG. 7B, a resist film 43 formed on theshielding film material 19′ is selectively patterned as follows.

[0092] First, a resist material is coated over the entire surface of theshielding film material 19′, and then exposed and developed by using, asa mask, a reticle having a predetermined aperture pattern formed bybaking. The aperture pattern has a shape for forming the light receivingwindows 21 shown in FIG. 7B above the photodiodes PD. Then, theexcessive resist material is removed to pattern the resist film 43.

[0093] Then, the shielding film material 19′ is selectively etchedthrough the resist film 43 used as the mask. The etching is anisotropicdry etching. As a result, as shown in FIG. 8A, the peripheries of thetransfer electrodes 17 can be covered without contact with therefractive index matching films 16 above the photodiodes PD. The reasonfor preventing contact between the shielding film material 19′ and therefractive index matching films 16 is to prevent a smear. When theshielding film material 19′ is overlapped with the refractive indexmatching film 16, a smear occurs.

[0094] Then, the cover film 22 comprising, for example, a BPSG film isformed over the entire surface of the silicon substrate 11 on which theshielding film 19 is formed. The BPSG film is used as the cover film 22.In order to shape the BPSG film used as the cover film 22, a reflow stepis performed. In this step, a heat treatment temperature is about 800°C. In the reflow step, the BPSG film is made convex in the interfacialdirection to form an original shape of a lens referred to as a layerlens. Then, as shown in FIG. 8B, the planarizing film 23 is formed overthe entire surface of the silicon substrate 11, and the color filterlayer 24 and the microlenses 25 are formed. The forming step is finishedto complete the photoelectric transducer 100 shown in FIG. 1.

[0095] The above-described method of manufacturing the photoelectrictransducer 100 of the first embodiment of the present invention iscapable of manufacturing the photoelectric transducer 100 with highreproducibility, in which the refractive index of the compound layer 16′serving as each refractive index matching film 16 is continuouslychanged from the refractive index of the silicon oxide film of 1.45 tothe refractive index of the silicon nitride film of 2.0, as comparedwith the case in which a silicon nitride single film and a silicon oxidesingle film are simply laminated.

[0096] Therefore, the refractive index can be continuously changed inthe order of the refractive index of the cover film 22, the refractiveindex of the top of the refractive index matching film 16, therefractive index of the bottom of the refractive index matching film 16,and the refractive index of the anti-reflection film 15, and the totalrefractive index can be changed in an analogue manner. Thus, thephotoelectric transducer 100 having high reliability can be provided, ascompared with a case in which films having different refractive indexesare laminated.

[0097] In this embodiment, the oxygen content of the compound layer isthe lowest at the interface with each light receiving element and thehighest in the upper portion of the compound layer, and the nitrogencontent of the compound layer is the highest at the interface with eachlight receiving element and the lowest in the upper portion of thecompound layer. However, the lowest oxygen content and the highestnitrogen content are not strictly at the interface with each lightreceiving element. Even when the oxygen and nitrogen contents arerespectively the lowest and the highest near the interface with eachlight receiving element, the same effect as described above can beexhibited. Namely, the highest oxygen content may be set at a positionabove the position of the highest nitrogen content. Also, the oxygen andnitrogen contents are not necessarily continuously changed over theentire region of the compound layer, but the oxygen or nitrogen contentmay be constant in a region of the compound layer.

[0098] Second Embodiment

[0099]FIG. 9 is a sectional view showing an example of a structure of aphotoelectric transducer 200 according to a second embodiment of thepresent invention.

[0100] The photoelectric transducer 200 shown in FIG. 9 is anotherexample of semiconductor devices, in which a refractive index matchingfilm 16 is formed directly on the silicon interface of each photodiodePD, and a silicon nitride single film and a gate insulating film 14 areomitted from the silicon interface so that the refractive index matchingfilm 16 also performs the function as an anti-reflection film 15, unlikein the photoelectric transducer 100 of the first embodiment.

[0101] The photoelectric transducer 200 is preferably applied to aphotocoupler, a solid-state imaging device or field-effect imagingdevice comprising a solid-state imaging device which receives lightincident from on-chip lenses provided on a color filter. Thephotoelectric transducer 200 comprises, for example, a N-type siliconsubstrate 11. Like in the first embodiment, the silicon substrate 11comprises a plurality of HAD (Hole Accumulated Diode) sensors (simplyreferred to as “photodiodes PD” hereinafter) In this embodiment, thephotodiode PD (charge coupled imaging device) of one pixel is described.

[0102] In the photoelectric transducer 200, a P-type impurity buriedlayer (P-WELL) 1 is provided on the N-type silicon substrate 11. TheP-WELL 1 contains the photodiode PD comprising a N-type impurity region(layer) 2, and a vertical CCD section 12 comprising a N-type impurityregion (layer) 3. Furthermore, the photodiode PD is separated from thevertical CCD section 12 by a transfer gate 13 so as to read a signalcharge from the photodiode PD to the vertical CCD section 12.

[0103] Furthermore, a silicon oxide film (SiO₂ film) serving as a gateinsulating film 14 having a predetermined thickness is provided on theinterface of the silicon substrate 11. However, unlike in the firstembodiment, the single-layer gate insulating film 14 and silicon nitridefilm are not provided on the photodiode PD. Namely, the refractive indexmatching film 16 having a thickness of about 1.0 μm to 2.0 μm isprovided directly on the photodiode PD. Namely, the bottom composed ofsilicon nitride in the refractive index matching film 16 functions asthe anti-reflection film 15.

[0104] Like in the first embodiment, the refractive index matching film16 comprises an insulating compound layer 16′ represented bySiO_(x)N_(y) (0≦x and y) assuming that the molar ratio of silicon,oxygen and nitrogen of the insulating compound layer 16′ is 1:x:y. Theoxygen content of the insulating compound layer 16′ is the lowest at thesilicon interface with the photodiode PD and the highest in au upperportion of the compound layer 16′, and the nitrogen content of theinsulating compound layer is the highest at the silicon interface withthe photodiode PD and the lowest in the upper portion of the compoundlayer 16′.

[0105] The refractive index matching film 16 comprises the bottomcomposed of silicon nitride, and the top composed of silicon oxide.Although the insulating compound layer 16′ may comprise a plurality ofinsulating layers having a constant thickness, the insulating compoundlayer 16′ preferably comprises layers having thicknesses continuouslyvarying to satisfy the above-described conditions of the nitrogen andoxygen contents. In this case, reflection within the layer can beminimized.

[0106] In the refractive index matching film 16, the oxygen content ofthe compound layer 16′ is defined in the range of 0≦x<2 so that theoxygen content is the lowest at the silicon interface with thephotodiode PD and the highest in the upper portion, and the nitrogencontent of the compound layer 16′ is defined in the range of 0≦y<4/3 sothat the nitrogen content is the highest at the silicon interface withthe photodiode PD and the lowest in the upper portion.

[0107] Namely, in the compound layer 16′, oxygen is continuouslydistributed based on the oxygen content condition of 0≦x<2 so that theoxygen content is the lowest at the silicon interface with thephotodiode PD and the highest in the upper portion. Also, in thecompound layer 16′, nitrogen is continuously distributed based on thenitrogen content condition 0≦y<4/3 so that the nitrogen content is thehighest at the silicon interface with the photodiode PD and the lowestin the upper portion.

[0108] Like in the first embodiment, the insulating compound layer 16′is preferably deposited by the low-pressure CVD apparatus 30. In thedeposition, an oxygen gas flow rate is controlled according to acontinuous increasing function (including primary and secondaryfunctions). At the same time, a nitrogen gas flow rate is controlledaccording to a decreasing function (including primary and secondaryfunctions). In this embodiment, the compound layer 16′ represented bySiO_(x)N_(y) satisfies 4=2x+3y, and x increases from the bottom to thetop.

[0109] Furthermore, like in the first embodiment, a transfer electrode17 is formed on the vertical CCD section 12 through the silicon oxidefilm. The transfer electrode 17 is covered with a shielding film 19composed of aluminum or tungsten through an interlayer insulating film18. The shielding film 19 has an aperture formed above the photodiodePD. The aperture functions as a light receiving window 21. The shieldingfilm 19 is coated with a cover film 22 comprising a silicon oxide filmof PSG or the like.

[0110] In this way, in the photoelectric transducer 200 of the secondembodiment of the present invention, the refractive index matching film16 is provided directly on the silicon interface of the photodiode PD,and the refractive index of the compound layer 161 serving as therefractive index matching film 16 can be continuously changed from therefractive index of the silicon oxide film of 1.45 to the refractiveindex of the silicon nitride film of 2.0, as compared with a case inwhich a silicon nitride single film and a silicon oxide single film aresimply laminated. Therefore, a boundary between the silicon nitride filmand the silicon oxide film is absent, thereby minimizing reflection fromthe photodiode PD.

[0111] Therefore, multiple reflection is decreased to improve lightreceiving sensitivity, as compared with the case in which the siliconnitride single film and the silicon oxide single film are simplylaminated. Furthermore, diffused reflection due to multiple reflectioncan be suppressed to improve a smear. The refractive index matching film16 comprising the insulating compound layer 16′ causes no stress, andthus causes less dark current.

[0112] Method of Manufacturing Semiconductor Device

[0113] FIGS. 10 to 13 are drawings showing steps (first to fourth) in anexample of the formation of the photoelectric transducer 200 of thesecond embodiment of the present invention.

[0114] This embodiment is based on the condition that the photoelectrictransducer 200 shown in FIG. 9 is manufactured. Under this manufacturingcondition, the silicon substrate 11 (semiconductor wafer 11′) having thetransfer electrode 17 and the photoelectric conversion photodiode PDshown in FIG. 10A is first prepared.

[0115] Referring to FIG. 10A, the gate insulating film 14 and theanti-reflection film 15 are not provided on the photodiodes PD. In thesemiconductor wafer 11′, a predetermined impurity is implanted into theN-type silicon substrate 11 shown in FIG. 10A to form the P-typesemiconductor buried layer (P-WELL) 1 in which the photodiode PDcomprising the N-type impurity region (layer) 2 and the vertical CCDsection 12 comprising the N-type impurity region (layer) 3 are formed.

[0116] In this structure, the transfer gate section 13 is formed as aregion for reading a signal charge from the photodiode PD to thevertical CCD section 12. Furthermore, polysilicon is deposited over theentire surface of the gate insulating film 14, and then selectivelyetched to form the transfer electrode 17.

[0117] Then, as shown in FIG. 10B, the semiconductor wafer 11′ isre-oxidized to form the interlayer insulating film 18 comprising asilicon oxide film. In this step, the oxide film is completely removedfrom the silicon interface of the photodiode PD by a plurality of timesof dry or wet etching. The transfer electrode 17 can be isolated by theinterlayer insulating film 18.

[0118] Then, as shown in FIG. 11A, the insulating compound layer 16′ isselectively formed over the entire surface of the semiconductor wafer11′ to form the refractive index matching film 16. Since the thicknessof the compound layer 161 must be strictly controlled, the compoundlayer 16′ is formed by the low-pressure CVD apparatus 30 shown in FIG.4. The refractive index matching film 16 comprises the bottom composedof silicon nitride in contact with the silicon interface of thephotodiode PD, and the top composed of silicon oxide.

[0119] Therefore, the refractive index matching film 16 comprises theinsulating compound layer 16′ represented by SiO_(x)N_(y) (0≦x and y)assuming that the molar ratio of silicon, oxygen and nitrogen of theinsulating compound layer 16′ is 1:x:y. In addition, the oxygen contentof the compound layer 16′ is the lowest at the silicon interface withthe photodiode PD and the highest in the upper portion of the compoundlayer 16′, and the nitrogen content of the compound layer 16′ is thehighest at the interface with the photodiode PD and the lowest in theupper portion of the compound layer 16′.

[0120] In forming the refractive index matching film 16, in order to setthe oxygen content of the compound layer 16′ to the lowest at thesilicon interface with the photodiode PD and the highest in the upperportion of the compound layer 16′, the oxygen content in the compoundlayer 16′ is defined in the range of 0≦x<2. Similarly, in order to setthe nitrogen content of the compound layer 16′ to the highest at theinterface with the photodiode PD and the lowest in the upper portion ofthe compound layer 16′, the nitrogen content in the compound layer 16′is defined in the range of 0≦y<4/3.

[0121] In order to continuously change the oxygen and nitrogen contentsof the compound layer 16′, the nitrogen and oxygen flow rates in thelow-pressure CVD apparatus 30 may be continuously changed during theformation of the film 16. Namely, in order to set the oxygen content ofthe compound layer 16′ to the lowest at the silicon interface with thephotodiode PD and the highest in the upper portion of the compound layer16′, the oxygen flow rate is regulated to continuously distribute basedon the oxygen content of 0≦x<2 in the compound layer 16′.

[0122] In order to set the nitrogen content of the compound layer 16′ tothe highest at the silicon interface with the photodiode PD and thelowest in the upper portion of the compound layer 16′, the nitrogen flowrate is regulated to continuously distribute based on the oxygen contentof 0≦y<4/3 in the compound layer 16′. In this example, the compoundlayer represented by SiO_(x)N_(y) satisfies 4=2x+3y, and x increasesfrom the bottom to the top.

[0123] Then, as shown in FIG. 11A, a resist film 42 formed on thecompound layer 16′ is selectively patterned as follows. First, a resistmaterial is coated over the entire surface of the compound layer 16′,and then exposed and developed by using, as a mask, a reticle having apredetermined aperture pattern formed by baking. The aperture patternhas a shape for forming the light receiving windows 21 above thephotodiodes PD. Then, the excess resist material is removed to patternthe resist film 42.

[0124] Then, the compound layer 16′ is selectively etched through theresist film 42 used as the mask. The etching may be wet etching or dryetching. The wet etching is performed with an etchant comprising dilutedhydrofluoric acid or phosphoric acid. As a result, as shown in FIG. 11B,the compound layer 16′ (film) can be left only above the photodiode PD,to form the refractive index matching film 16.

[0125] Then, as shown in FIG. 12A, aluminum or tungsten used as amaterial 19′ for the shielding film 19 is deposited over the entiresurface of the silicon substrate 11 by the same method as a conventionalmethod. Then, as show in FIG. 12B, a resist film 43 formed on theshielding film material 19′ is selectively patterned as follows.

[0126] First, a resist material is coated over the entire surface of theshielding film material 19′, and then exposed and developed by using, asa mask, a reticle having a predetermined aperture pattern formed bybaking. The aperture pattern has a shape slightly larger than a shapefor forming the light receiving windows 21 above the photodiodes PD.Then, the excess resist material is removed to pattern the resist film43.

[0127] Then, the shielding film material 19′ is selectively etchedthrough the resist film 43 used as the mask. The etching is anisotropicdry etching. As a result, as shown in FIG. 13A, the peripheries of thetransfer electrodes 17 can be covered without contact with therefractive index matching films 16 above the photodiodes PD. The reasonfor preventing contact between the shielding film material 19′ and therefractive index matching film 16 is to prevent a smear. When theshielding film material 19′ is overlapped with the refractive indexmatching film 16, a smear occurs.

[0128] Then, the cover film 22 comprising, for example, a BPSG film, isformed over the entire surface of the silicon substrate 11 on which theshielding film 19 is formed. In order to shape the BPSG film, a reflowstep is performed. In this step, a heat treatment temperature is about800° C. In the reflow step, the BPSG film is made convex in theinterfacial direction to form an original shape of a lens referred to asa layer lens. Then, as shown in FIG. 13B, the planarizing film 23 isformed over the entire surface of the silicon substrate 11, the colorfilter 24, and the microlenses 25 are formed. The forming step isfinished to complete the photoelectric transducer 200 shown in FIG. 9.

[0129] The above-described method of manufacturing the photoelectrictransducer 200 of the second embodiment of the present invention iscapable of manufacturing the photoelectric transducer 200 with highreproducibility, in which the refractive index matching film isdeposited directly on the silicon interface of the photodiode PD, andthus the refractive index of the compound layer 16′ serving as therefractive index matching film 16 is continuously changed from therefractive index of the silicon oxide film of 1.45 to the refractiveindex of the silicon nitride film of 2.0, as compared with the case inwhich a silicon nitride single film and a silicon oxide single film aresimply laminated.

[0130] Therefore, the refractive index can be continuously changed inthe order of the refractive index of the cover film 22, the refractiveindex of the top of the refractive index matching film 16, therefractive index of the bottom of the refractive index matching film 16,and the refractive index of the anti-reflection film 15, and the totalrefractive index can be changed in an analogue manner. Thus, thephotoelectric transducer 200 having high reliability can be provided, ascompared with the case in which films having different refractiveindexes are laminated.

[0131] In this embodiment, the oxygen content of the compound layer isthe lowest at the interface with each light receiving element and thehighest in the upper portion of the compound layer, and the nitrogencontent of the compound layer is the highest at the interface with eachlight receiving element and the lowest in the upper portion of thecompound layer. However, the lowest oxygen content and the highestnitrogen content are not strictly at the interface with each lightreceiving element. Even when the oxygen and nitrogen contents arerespectively the lowest and the highest near the interface with eachlight receiving element, the same effect as described above can beexhibited. Namely, the highest oxygen content may be set at a positionabove the position of the highest nitrogen content. Also, the oxygen andnitrogen contents are not necessarily continuously changed over theentire region of the compound layer, but the oxygen or nitrogen contentmay be constant in a region of the compound layer.

[0132] As described above, in a semiconductor device of the firstembodiment of the present invention, an insulating compound layer isprovided on a semiconductor substrate, and the insulating compound layeris represented by SiO_(x)N_(y) (0≦x and y) assuming that the molar ratioof silicon, oxygen and nitrogen of the insulating compound layer is1:x:y. The oxygen content of the insulating compound layer is the lowestat the interface with the semiconductor substrate and the highest in anupper portion of the compound layer, and the nitrogen content of theinsulating compound layer is the highest at the interface with thesemiconductor substrate and the lowest in the upper portion of thecompound layer.

[0133] In this structure, the refractive index of the compound layerserving as a refractive index matching film can be continuously changedfrom the refractive index of a silicon oxide film of 1.45 to therefractive index of a silicon nitride film of 2.0, as compared with acase in which a silicon nitride single film and a silicon oxide singlefilm are simply laminated. Therefore, a boundary between the siliconnitride film and the silicon oxide film can be removed, therebyminimizing reflection on the light receiving element.

[0134] In the semiconductor device of the second embodiment of thepresent invention, the insulating compound layer of the semiconductordevice of the first embodiment is used as a refractive index matchingfilm. Namely, the refractive index matching film is provided on thephotoelectric conversion light receiving element, and the refractiveindex matching film comprises the insulating compound layer representedby SiO_(x)N_(y) (0≦x and y) assuming that the molar ratio of silicon,oxygen and nitrogen of the insulating compound layer is 1:x:y. Theoxygen content of the insulating compound layer is the lowest at theinterface with the light receiving element and the highest in au upperportion of the compound layer, and the nitrogen content of theinsulating compound layer is the highest at the interface with the lightreceiving element and the lowest in the upper portion of the compoundlayer.

[0135] In this structure, the refractive index of the compound layerserving as the refractive index matching film can be continuouslychanged from the refractive index of a silicon oxide film of 1.45 to therefractive index of a silicon nitride film of 2.0, as compared with acase in which a silicon nitride single film and a silicon oxide singlefilm are simply laminated. Therefore, a boundary between the siliconnitride film and the silicon oxide film can be removed, therebyminimizing reflection from the light receiving element. Therefore,multiple reflection is decreased to improve light receiving sensitivity,as compared with the case in which the silicon nitride single film andthe silicon oxide single film are simply laminated. Furthermore,diffused reflection due to multiple reflection can be suppressed toimprove a smear.

[0136] In the method of manufacturing the semiconductor device of thepresent invention, a plurality of photoelectric conversion lightreceiving elements are formed on the semiconductor substrate, and thenthe refractive index matching film is formed on the light receivingelements on the semiconductor substrate. The refractive index matchingfilm comprises the insulating compound layer represented by SiO_(x)N_(y)(0≦x and y) assuming that the molar ratio of silicon, oxygen andnitrogen of the insulating compound layer is 1:x:y. The oxygen contentof the insulating compound layer is the lowest at the interface witheach light receiving element and the highest in au upper portion of thecompound layer, and the nitrogen content of the insulating compoundlayer is the highest at the interface with each light receiving elementand the lowest in the upper portion of the compound layer.

[0137] This method is capable of manufacturing the semiconductor devicewith high reproducibility in which the refractive index of the compoundlayer serving as the refractive index matching film can be continuouslychanged from the refractive index of a silicon oxide film of 1.45 to therefractive index of a silicon nitride film of 2.0, as compared with acase in which a silicon nitride single film and a silicon oxide singlefilm are simply laminated. Therefore, the semiconductor device with highreliability can be provided.

[0138] The apparatus for manufacturing the semiconductor device of thepresent invention comprises deposition means for depositing therefractive index matching film on the light receiving elements formed onthe semiconductor substrate. The refractive index matching filmdeposited by the deposition means comprises the insulating compoundlayer represented by SiO_(x)N_(y) (0≦x and y) assuming that the molarratio of silicon, oxygen and nitrogen of the insulating compound layeris 1:x:y. The oxygen content of the insulating compound layer is thelowest at the interface with each light receiving element and thehighest in au upper portion of the compound layer, and the nitrogencontent of the insulating compound layer is the highest at the interfacewith each light receiving element and the lowest in the upper portion ofthe compound layer.

[0139] This apparatus is capable of manufacturing the semiconductordevice with high reproducibility in which the refractive index of thecompound layer serving as the refractive index matching film can becontinuously changed from the refractive index of a silicon oxide filmof 1.45 to the refractive index of a silicon nitride film of 2.0, ascompared with a case in which a silicon nitride single film and asilicon oxide single film are simply laminated. Therefore, thesemiconductor device with high reliability can be provided.

[0140] The present invention is preferably applied to a photoelectricconversion device such as a photocoupler or the like, a solid stateimaging device or field effect imaging device comprising a semiconductorimaging device for receiving light incident from an on-chip lensprovided on a color filter.

What is claimed is:
 1. A semiconductor device comprising: a substrate;and a compound layer provided on the substrate, wherein the compoundlayer is represented by SiO_(x)N_(y) (0≦x and y) assuming that the molarratio of silicon, oxygen and nitrogen of the compound layer is 1:x:y,the oxygen content is the lowest near the interface with the substrateand the highest in an upper portion of the compound layer, and thenitrogen content is the highest near the interface with the substrateand the lowest in the upper portion of the compound layer.
 2. Asemiconductor device according to claim 1, wherein the compound layerincludes a region having a constant oxygen or nitrogen content.
 3. Asemiconductor device according to claim 1, wherein the substratecomprises a light receiving element formed near the interface with thecompound layer, and an insulating film.
 4. A semiconductor devicecomprising: a semiconductor substrate; and an insulating compound layerprovided on the semiconductor substrate, wherein the insulating compoundlayer is represented by SiO_(x)N_(y) (0≦x and y) assuming that the molarratio of silicon, oxygen and nitrogen of the insulating compound layeris 1:x:y, the oxygen content is the lowest at the interface with thesemiconductor substrate and the highest in an upper portion of theinsulating compound layer, and the nitrogen content is the highest atthe interface with the semiconductor substrate and the lowest in theupper portion of the insulating compound layer.
 5. A semiconductordevice according to claim 4, wherein the oxygen content of the compoundlayer is in the range of 0≦x<2 in order to set the oxygen content of thecompound layer to the lowest at the interface with the semiconductorsubstrate and the highest in the upper portion of the compound layer,and the nitrogen content of the compound layer is defined in the rangeof 0≦y<4/3 in order to set the nitrogen content of the compound layer tothe highest at the interface with the semiconductor substrate and thelowest in the upper portion of the compound layer.
 6. A semiconductordevice according to claim 4, wherein the oxygen content is continuouslydistributed in the compound layer based on the range of 0≦x<2 in orderto set the oxygen content of the compound layer to the lowest at theinterface with the semiconductor substrate and the highest in the upperportion of the compound layer, and the nitrogen content is continuouslydistributed in the compound layer based on the range of 0≦y<4/3 in orderto set the nitrogen content of the compound layer to the highest at theinterface with the semiconductor substrate and the lowest in the upperportion of the compound layer.
 7. A semiconductor device according toclaim 4, wherein the compound layer represented by SiO_(x)N_(y)satisfies 4=2x+3y, and x increases from the bottom to the top.
 8. Asemiconductor device for photoelectrically converting received light tooutput a received light signal comprising: a semiconductor substrate; aplurality of light receiving elements for photoelectric conversion,which are provided on the semiconductor substrate; and a refractiveindex matching film provided on each of the light receiving elements,wherein the refractive index matching film comprises a compound layerrepresented by SiO_(x)N_(y) (0≦x and y) assuming that the molar ratio ofsilicon, oxygen and nitrogen of the compound layer is 1:x:y, the oxygencontent of the compound layer is the lowest at the interface with eachlight receiving element and the highest in an upper portion of thecompound layer, and the nitrogen content of the compound layer is thehighest at the interface with each light receiving element and thelowest in the upper portion of the compound layer.
 9. A semiconductordevice according to claim 8, wherein in the refractive index matchingfilm, the oxygen content of the compound layer is in the range of 0≦x<2in order to set the oxygen content to the lowest at the interface witheach light receiving element and the highest in the upper portion of thecompound layer, and the nitrogen content of the compound layer is in therange of 0≦y<4/3 in order to set the nitrogen content to the highest atthe interface with each light receiving element and the lowest in theupper portion of the compound layer.
 10. A semiconductor deviceaccording to claim 8, wherein the oxygen content is continuouslydistributed in the compound layer based on the range of 0≦x<2 in orderto set the oxygen content of the compound layer to the lowest at theinterface with each light receiving element and the highest in the upperportion of the compound layer, and the nitrogen content is continuouslydistributed in the compound layer based on the range of 0≦y<4/3 in orderto set the nitrogen content of the compound layer to the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.
 11. A semiconductor device according toclaim 8, wherein the compound layer represented by SiO_(x)N_(y)satisfies 4=2x+3y, and x increases from the bottom to the top.
 12. Asemiconductor device according to claim 8, wherein the bottom of therefractive index matching film comprises silicon nitride Si₃N₄.
 13. Asemiconductor device according to claim 8, wherein the top of therefractive index matching film comprises silicon oxide SiO₂.
 14. Asemiconductor device according to claim 8, further comprising a siliconoxide film having a predetermined thickness and provided between thelight receiving elements and the refractive index matching films.
 15. Asemiconductor device according to claim 14, wherein the thickness t ofthe silicon oxide film is in the range of 10 nm≦t≦40 nm.
 16. A method ofmanufacturing a semiconductor device for photoelectrically convertingreceived light to output a received light signal, the method comprising:a step of forming a plurality of photoelectric conversion lightreceiving elements on a semiconductor substrate; and a step of forming arefractive index matching film on each of the light receiving elementsformed on the semiconductor substrate, wherein the refractive indexmatching film comprises an insulating compound layer represented bySiO_(x)N_(y) (0≦x and y) assuming that the molar ratio of silicon,oxygen and nitrogen of the insulating compound layer is 1:x:y, theoxygen content of the compound layer is the lowest at the interface witheach light receiving element and the highest in an upper portion of thecompound layer, and the nitrogen content of the compound layer is thehighest at the interface with each light receiving element and thelowest in the upper portion of the compound layer.
 17. A method ofmanufacturing a semiconductor device according to claim 16, wherein informing the refractive index matching film, the oxygen content of thecompound layer is in the range of 0≦x<2 in order to set the oxygencontent to the lowest at the interface with each light receiving elementand the highest in the upper portion of the compound layer, and thenitrogen content of the compound layer is in the range of 0≦y<4/3 inorder to set the nitrogen content to the highest at the interface witheach light receiving element and the lowest in the upper portion of thecompound layer.
 18. A method of manufacturing a semiconductor deviceaccording to claim 16, wherein the oxygen content is continuouslydistributed in the compound layer based on the range of 0≦x<2 in orderto set the oxygen content of the compound layer to the lowest at theinterface with each light receiving element and the highest in the upperportion of the compound layer, and the nitrogen content is continuouslydistributed in the compound layer based on the range of 0≦y<4/3 in orderto set the nitrogen content of the compound layer to the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.
 19. A method of manufacturing asemiconductor device according to claim 16, wherein the compound layerrepresented by SiO_(x)N_(y) satisfies 4=2x+3y, and x increases from thebottom to the top.
 20. A method of manufacturing a semiconductor deviceaccording to claim 16, wherein the refractive index mating filmcomprises the bottom composed of silicon nitride in contact with thelight receiving elements, and the top composed of silicon oxide.
 21. Amethod of manufacturing a semiconductor device according to claim 16,further comprising a step of forming a silicon oxide film having apredetermined thickness on the light receiving elements before formingthe refractive index matching films on the light receiving elements. 22.A method of manufacturing a semiconductor device according to claim 21,wherein the thickness t of the silicon oxide film is in the range of 10nm≦t≦40 nm.
 23. An apparatus for manufacturing a semiconductor devicefor photoelectrically converting received light to output a receivedlight signal, the apparatus comprising: a formation means for forming aplurality of photoelectric conversion light receiving elements on asemiconductor substrate; and a deposition means for depositing arefractive index matching film on each of the light receiving elementsformed on the semiconductor substrate, wherein in depositing therefractive index matching film by the deposition means, an insulatingcompound layer represented by SiO_(x)N_(y) (0≦x and y) assuming that themolar ratio of silicon, oxygen and nitrogen of the insulating compoundlayer is 1:x:y is deposited so that the oxygen content of the compoundlayer is the lowest at the interface with each light receiving elementand the highest in an upper portion of the compound layer, and thenitrogen content of the compound layer is the highest at the interfacewith each light receiving element and the lowest in the upper portion ofthe compound layer.
 24. An apparatus manufacturing a semiconductordevice according to claim 23, wherein in forming the refractive indexmatching film, the oxygen content of the compound layer is previouslydefined in the range of 0≦x<2 in order to set the oxygen content to thelowest at the interface with each light receiving element and thehighest in the upper portion of the compound layer, and the nitrogencontent of the compound layer is previously defined in the range of0≦y<4/3 in order to set the nitrogen content to the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.
 25. An apparatus for manufacturing asemiconductor device according to claim 23, wherein the compound layerrepresented by SiO_(x)N_(y) satisfies 4=2x+3y, and x increases from thebottom to the top.
 26. An apparatus for manufacturing a semiconductordevice according to claim 23, wherein in the deposition means, an oxygenflow rate is continuously regulated based on the oxygen content of 0≦x<2in order to set the oxygen content of the compound layer to the lowestat the interface with each light receiving element and the highest inthe upper portion of the compound layer, and a nitrogen flow rate iscontinuously regulated based on the nitrogen content of 0≦y<4/3 in orderto set the nitrogen content of the compound layer to the highest at theinterface with each light receiving element and the lowest in the upperportion of the compound layer.
 27. An apparatus for manufacturing asemiconductor device according to claim 23, wherein the deposition meansuses a low-pressure CVD apparatus.